1. Field of the Invention
The present invention relates to a sewing machine for stitching.
2. Description of the Prior Art
FIG. 1 shows in cross section a typical prior art construction of a horizontal axis full rotary loop taker including a hook body 1 and a bobbin case holder 2 supported in the hook body 1. A bobbin case 5 indicated by imaginary lines is mounted in the bobbin case holder 2, the bobbin case 5 accommodating a bobbin 4 on which is wound thread 3. The hook body 1 is secured to a horizontally extending lower shaft 6 of a sewing machine and is rotated thereby. A needle 7 reciprocates up and down in directions indicated by arrow 8, the lowermost point of the path of travel of the needle 7 being indicated by reference numeral 9. The axis of rotation of the bobbin 4 is aligned with or parallel to the axis of the lower shaft 6. In the thus constructed horizontal axis full rotary loop taker, a bobbin case holder rib 10 formed on the outer circumferential surface of the bobbin case holder 2 engages with a hook groove 11 formed in the hook body 1. As the hook body 1 is rotated, an upper thread loop is seized by a loop seizing hook or beak 16 and is moved slidingly along a bottom 14 of the bobbin case holder 2 while contacting the lower part of the bottom 14 of the bobbin case holder 2, thus accomplishing a thread cast-off operation.
In the above prior art arrangement, if the amount of the thread loaded on the bobbin 4 is to be increased, it is necessary to extend the axial length H of the bobbin 4. There are two possible methods of extending the axial length H of the bobbin 4, that is, (a) to extend the bobbin 4 in the direction toward the open end of the bobbin case holder 2 (in the rightward direction in FIG. 1) or (b) to enlarge the bottom 14 of the bobbin case holder 2 in the leftward direction in FIG. 1 and extend the bobbin 4 in the direction toward the bottom 14.
If the bobbin 4 is extended in the direction toward the open end of the bobbin case holder 2 in accordance with the above method (a), when the needle 7 moves down to its lowermost point 9, the needle point is positioned inwardly of the peripheral surface of the mass of bobbin thread 3 wound on the bobbin 4, causing the needle 7 to stick into the thread 3 wound on the bobbin 4 and thereby breaking the thread 3 wound on the bobbin 4. On the other hand, if the bottom 14 of the bobbin case holder 2 is extended in the leftward direction in FIG. 1, the thread on the needle will be caught on the lower part of the bottom 14 of the bobbin case holder 2, thus preventing the cast-off operation of the thread and therefore stopping the sewing operation.